Efficient use of grassland nitrogen

Summary

In nitrate sensitive areas with agricultural production the recommended upper limit of nitrate in percolation water is 50 mg per litre. Organic farming has a lower nitrate leaching potential compared to conventional farming, but may occasionally exceed this limit, especially in the case of dairy crop rotations. In such rotations a considerable build-up of N takes place in grazed grassland. Therefore, organic dairy farming may only present an opportunity to reduce nitrate leaching if this grassland N is efficiently utilised. Losses may occur during grazing, and ploughing of grassland is followed by a large increase in the mineralization of N that often exceeds the need of the subsequent arable crop.
An experimental site at Research Centre Foulum has since 1997 been dedicated to studies on the utilization of grassland nitrogen in organic dairy systems. Different aspects have been studied and new investigations are in progress. Some of the main themes are described here in relation mainly to the effects observed on residual fertilizer effects and leaching losses.